device: add Device.ListenPort and Device.SetListenPortjs/sample-api

This is a sample commit for a possible way to make
a Go API that lives alongside UAPI.

The general idea is to add Device and Peer methods
corresponding to UAPI directives, including a way to
look up a peer from a device based on a public key,
as in UAPI.

The UAPI code then deals with parsing and generating textual
input/output, and calls the Go methods to do the work.

This commit also contains a bug fix for a racy access of device.net.port
I will send an independently commit that fixes those directly in UAPI.
This commit is NOT meant to be merged as-is.

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

2 files changed, 24 insertions, 9 deletions

diff --git a/device/device.go b/device/device.go
index 5f128fc..f7885ce 100644
--- a/device/device.go
+++ b/device/device.go
@@ -90,6 +90,23 @@ type Device struct {
 	}
 }
 
+// ListenPort returns the port that device is listening on.
+// It returns 0 if the device is not listening on any ports.
+func (device *Device) ListenPort() uint16 {
+	device.net.Lock()
+	defer device.net.Unlock()
+	return device.net.port
+}
+
+// SetListenPort sets the port that the device is listening on.
+// The new port is bound immediately.
+func (device *Device) SetListenPort(port uint16) error {
+	device.net.Lock()
+	defer device.net.Unlock()
+	device.net.port = port
+	return device.bindUpdateLocked()
+}
+
 // An encryptionQueue is a channel of QueueOutboundElements awaiting encryption.
 // An encryptionQueue is ref-counted using its wg field.
 // An encryptionQueue created with newEncryptionQueue has one reference.
@@ -490,9 +507,12 @@ func (device *Device) BindSetMark(mark uint32) error {
 }
 
 func (device *Device) BindUpdate() error {
-
 	device.net.Lock()
 	defer device.net.Unlock()
+	return device.bindUpdateLocked()
+}
+
+func (device *Device) bindUpdateLocked() error {
 
 	// close existing sockets
 
diff --git a/device/uapi.go b/device/uapi.go
index 2843a4c..3575c11 100644
--- a/device/uapi.go
+++ b/device/uapi.go
@@ -58,8 +58,8 @@ func (device *Device) IpcGetOperation(w io.StringWriter) error {
 			send("private_key=" + device.staticIdentity.privateKey.ToHex())
 		}
 
-		if device.net.port != 0 {
-			send(fmt.Sprintf("listen_port=%d", device.net.port))
+		if port := device.ListenPort(); port != 0 {
+			send(fmt.Sprintf("listen_port=%d", port))
 		}
 
 		if device.net.fwmark != 0 {
@@ -162,12 +162,7 @@ func (device *Device) IpcSetOperation(r io.Reader) error {
 				// update port and rebind
 
 				logDebug.Println("UAPI: Updating listen port")
-
-				device.net.Lock()
-				device.net.port = uint16(port)
-				device.net.Unlock()
-
-				if err := device.BindUpdate(); err != nil {
+				if err := device.SetListenPort(uint16(port)); err != nil {
 					logError.Println("Failed to set listen_port:", err)
 					return &IPCError{ipc.IpcErrorPortInUse}
 				}